EDM pulse control: a design approach

The electro discharge machining operation has become relatively simple with the advent of CNC machines where the operator skills have been taken over by the skills built into the CNC. This is not so in the case of manual machines, where the operator skill is very critical to getting the final product finish; this being very true for a country like India, where most of the EDM users continue to use manual machines due to the prohibitive costs involved with CNC. An attempt has been made here to provide CNC like features in a manual ram type spark erosion machine at a fraction of the cost of a CNC, so that it is available to most of the users. One of the large hurdles in the EDM field is to ensure high material removal rates with better and predictable finishes and not getting the workpiece and tool damaged due to arcing or short-circuiting etc. This involves special waveforms to be produced for the eroding current, special h/w to take protective/corrective actions in case of a fault or an imminent fault and the presence of a good servo system. For this design, it is assumed that a good servo system is available and only the other two points are taken care of here. The scheme depicted involves the generation and alteration of the eroding current waveforms and the incorporation of special controls to take care of the fault conditions.